I've read a lot of criticism of Prince using "autotune" as chasing trends... I think I ever wrote some of them But upon more close listening I hear a difference between Prince's vocal effects... I'm not sure I'd call it straight up autotune in the way Kanye West or T-Pain is using it... because it sounds more like a portamento effect to me that bends pitches at the beginning and ending of notes to slide one note into another, as opposed to being used to keep a tune.

I don't know if that description makes sense, but Prince's use of the effect is not to "correct" his notes, but sounds like to me more like he is using it to bend the notes purposely at the beginning /end of them.

Anyone who's played around with a synthesizer portamento effect... do you hear the same thing?

Yeah, it's almost as if he is using the tremelo (whammy bar) to distort his voice as if it were a guitar note/string.